In a conventional dynamic focusing (CDF) where one scan line is configured by using single transmission/reception process, focused signals can be obtained in all regions on the scan line of a received beam. However, in the CDF, since single focusing point is fixed in the reception process, resolution is low in regions other than the focusing point.
On the other hand, in synthetic aperture (SA) beam forming, since the focused signal can be obtained in all the transmission and reception regions, high-resolution image can be obtained in comparison to the CDF.
In the synthetic aperture beam forming, transmission and reception processes are sequentially performed by using subapertures constructed with a certain number of conversion elements, and acquired reception signals are combined to each other with an optimum delay time being applied, so that each scan line is configured. Since an effect of focusing ultrasonic waves can be obtained by using a synthetic aperture corresponding to a total size of the subapertures used for configuring each scan line, resolution can be effectively improved. However, in the synthetic aperture beam forming, since signals transmitted and received by using several adjacent subapertures are used for configuring one scan line. Therefore, unlike the CDF, the synthetic aperture beam forming is very sensitive to shaking of ultrasonic wave converters, motion of an object, or motion of an organ in a human body, and the like. The above-mentioned motions lead to non-uniformity of acoustic characteristics in a humane organ and phase distortion of received echo signals, so that the performance of ultrasonic wave focusing is deteriorated. Therefore, in order to observe an image of a fast-moving object by using the synthetic aperture beam forming, the defects regarding to the motion need to be overcome.